Cell phone records of engineer Robert Sanchez, who was among the dead, show he sent a message after receiving one about a minute and 20 seconds before the crash, the National Transportation Safety Board said in a press release.

Investigators are looking into why Sanchez ran through a red signal and collided with a Union Pacific train Sept. 12 in Los Angeles’ San Fernando Valley. It was the nation’s deadliest rail crash since 1993.

Sanchez sent his last text message at 4:22:01 p.m. According to the freight train’s onboard recorder, the accident occurred at 4:22:23 p.m.

Records obtained from Sanchez’s cell phone provider also showed that he sent 24 text messages and received 21 messages over a two-hour period during his morning shift. During his afternoon shift, he received seven and sent five messages.

NTSB investigators were continuing to correlate times from Sanchez’s cell phone, the train recorders and data from the railroad signal system.

“I am pleased with the progress of this major investigation to date,” acting NTSB Chairman Mark V. Rosenker said in a statement. “We are continuing to pursue many avenues of inquiry to find what caused this accident and what can be done to prevent such a tragedy in the future.”

NTSB spokesman Terry Williams declined to release information about who was exchanging text messages with Sanchez.

In the days after the crash, several teenage train enthusiasts told a reporter Sanchez sent them a text message just before the collision. Federal investigators spurred by the media reports interviewed two 14-year-old boys, who they said cooperated in the investigation and provided their cell phone data.

The collision, which also injured more than 130 people, occurred on a horseshoe-shaped section of track in the community of Chatsworth. Investigators say the two trains were in sight of each other only for a few seconds before the crash. The freight engineer was able to apply brakes but brakes were never applied on the Metrolink train